<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>let 命令</title>
<script>
{
var x = 20;
 let y = 10;
 }
 console.log(x); // 20
 console.log(y); // ReferenceError: y is not defined
 </script>
 </head>
 <body></body>
 </html>